electrothermal propulsion

Electrothermal propulsion is a form of electric propulsion in which electrical
energy is used to heat a suitable propellant causing it to expand through
a supersonic nozzle and generate thrust. Two basic types of electrothermal
thruster are in use today: the resistojet and the arcjet. In both, material characteristics
limit the effective exhaust velocity to values similar to those of chemical
rockets. A third, experimental type is the microwave
plasma thruster which potentially could achieve somewhat higher exhaust
velocities.